The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP: third generation partnership project
CA: carrier aggregation
CH: cluster head (e.g., user equipment) of a cluster
C-RNTI: cell radio network temporary identifier
CS: carrier sensing
CSMA/CA: carrier sense multiple access with collision avoidance
CTS: clear-to-send
DCF: distributed coordination function
DIFS: DCF inter-frame space
D2D: device-to-device
eNB: evolved node B/base station in an E-UTRAN system
E-UTRAN evolved UTRAN (LTE)
FCS: frame check sequence
ISM: industrial, scientific, medical
LTE: long term evolution
LTE-A LTE-Advanced
NAV: net allocation vector
MAC medium access control
MTM: machine-to-machine
PCF: point coordination function
PIFS: PCF inter-frame space
RA: receiving STA address
RTS: request-to-send
SIFS: short inter-frame space
STA: station
TA: transmitting STA address
UE: user equipment
UTRAN universal terrestrial radio access network
Wireless data traffic is expected in the near future to more fully exploit license-exempt spectrum, sometimes termed shared frequency bands. For example, ISM (Industrial Scientific Medical) bands, which have 2.4 GHz or 5.8 GHz frequency bands, are shared bands.
The device-to-device (D2D) communication enables new service opportunities and reduces the eNB load for short range data intensive peer-to-peer communications. The possibility and benefits of the D2D communications as an underlay of an LTE-A (LTE-Advanced) network have been investigated and proved by some current literatures, e.g., see Chia-Hao Yu, Olav Tirkkonen, Klaus Doppler, et al., “On the performance of Device-to-Device underlay communication with simple power control”, IEEE 69th Vehicular Technology Conference, VTC '09, 1-5, Apr. 2009, and Klaus Doppler, Mika P. Rinne, Pekka Janis, et al., “Device-to-Device communications; functional prospects for LTE-Advanced networks”, IEEE International Conference on Communications Workshops, ICC '09, 1-6, Jun. 2009.
Furthermore, WLANs (wireless local area networks) become more and more popular in homes, offices, restaurants, shopping malls, etc. due to ease of installation and growing demand. The necessary and primary function in IEEE 802.11 WLAN infrastructures is a DCF (Distributed Coordination Function). This function does not have a center node to control the channel access. All stations (STAs) contend for the channel equally by using CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), as described, e.g., in the IEEE 802.11 specification: IEEE Std 802.11™-2007, “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”.
The basic CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) access for the DCF is shown in the FIG. 1: a STA senses the spectrum in a channel before starting any transmission. When the spectrum is free, the STA still wait for a DIFS (DCF inter-frame space) and a random back-off window to avoid multiple STAs transmitting the frame simultaneously. After the back-off window expires, the STA could access the channel.
The basic CSMA/CA cannot overcome a “hidden-terminal” problem. FIG. 2 illustrates such a problem. STA1 first senses the channel and finds that the channel is free, such that after DIFS and backoff window expire, it begins to transmit data to STA2. On the other hand, STA3 has already occupied the channel and is transmitting data to STA4. Due to path-loss, STA1 cannot hear STA3 but STA2 can hear STA3. As a result, the signals from STA1 and STA3 are collided. In order to solve this problem, an extended CSMA/CA mechanism is specified in the IEEE 802.11.
The extended CSMA/CA mechanism is a virtual CS (carrier sensing) mechanism by introducing a RTS (request-to-send) frame and a CTS (clear-to-send) frame and updating the NAV (network allocation vector) in all 802.11 STAs. Both RTS and CTS and other MAC frames contain a duration field which indicates how long the channel is busy. This is demonstrated in FIG. 3. The RTS and CTS frame structures are shown in FIG. 4, where RA, TA and FCS are fields indicating receiving station address, transmitting station address and frame check sequence, respectively.
Multiple radio systems, including LTE wireless systems (e.g., TDD (time division duplex) version of LTE known as TD-LTE) can operate in these frequency bands with the limitation that all the systems must follow the etiquette defined for the ISM band. How to coordinate band sharing with WLAN systems to avoid severe interference or contention is an important problem to be solved. The embodiments of the present invention provide a solution for such a challenge.